Utilizing reallocation via a decentralized, or distributed, agreement protocol (DAP) for storage unit (SU) replacement

ABSTRACT

Based on a system configuration change (e.g., of a Decentralized, or Distributed, Agreement Protocol (DAP)) within a dispersed storage network (DSN) (e.g., from a first to a second system configuration of the DAP), a computing device directs a storage unit to be replaced (SUTBR) to transfer encoded data slices (EDSs) stored therein to a replacement storage unit (RSU). During transfer of the EDSs (e.g., from SUTBR to RSU), the computing device directs the SUTBR to service read and/or write requests for EDS(s) stored therein to operate based on a first system configuration of the DAP. When the EDSs have been successfully transferred from the SUTBR to the RSU, the computing device directs the RSU to service read and/or write requests for the EDS(s) stored therein to operate based on a second system configuration of the DAP.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION Technical Field of the Invention

This invention relates generally to computer networks and moreparticularly to dispersing error encoded data.

Description of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on an Internetstorage system. The Internet storage system may include a RAID(redundant array of independent disks) system and/or a dispersed storagesystem that uses an error correction scheme to encode data for storage.

Within memory storage systems, there may be many reasons for a change ofthe number of storage units deployed therein. For example, there may beinstances in which a storage unit is replaced (e.g., the storage unit isperforming poorly, the storage unit is past a certain age at whichfailure is expected, etc.). When this happens, other devices in thesystem may need to coordinate with one another to accommodate not onlythe removal of the storage unit but also the bringing on line andintegration of a newly added storage unit to the overall system. Theprior art does not provide an adequate means by which such systemchanges, modification, etc. including the replacement of a storage unitmay be made without deleteriously affected overall system performance.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed ordistributed storage network (DSN) in accordance with the presentinvention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present invention;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present invention;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present invention;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present invention;

FIG. 6 is a schematic block diagram of an example of a slice name of anencoded data slice (EDS) in accordance with the present invention;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present invention;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present invention;

FIG. 9 is a schematic block diagram of an embodiment of Decentralized,or Distributed, Agreement Protocol (DAP) in accordance with the presentinvention;

FIG. 10 is a schematic block diagram of an example of creatingpluralities of sets of slices in accordance with the present invention;

FIG. 11 is a schematic block diagram of an example of storage vaults inaccordance with the present invention;

FIG. 12 is a schematic block diagram of an example of storingpluralities of sets of slices in accordance with the present invention;

FIG. 13 is a schematic block diagram of an example of adding a storagepool to the DSN in accordance with the present invention;

FIG. 14 is a schematic block diagram of an embodiment of adecentralized, or distributed, agreement protocol (DAP) for generatingidentified set of storage units in accordance with the presentinvention;

FIG. 15 is a schematic block diagram of an example of a replacement of astorage unit (SU) within a storage pool in accordance with the presentinvention;

FIG. 16A, FIG. 16B, and FIG. 16C are schematic block diagrams ofexamples of replacement of a SU within a storage pool in accordance withthe present invention; and

FIG. 17 is a diagram illustrating an embodiment of a method forexecution by one or more computing devices.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofcomputing devices 12-16, a managing unit 18, an integrity processingunit 20, and a DSN memory 22. The components of the DSN 10 are coupledto a network 24, which may include one or more wireless and/or wirelined communication systems; one or more non-public intranet systemsand/or public internet systems; and/or one or more local area networks(LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of storage units 36 that may belocated at geographically different sites (e.g., one in Chicago, one inMilwaukee, etc.), at a common site, or a combination thereof. Forexample, if the DSN memory 22 includes eight storage units 36, eachstorage unit is located at a different site. As another example, if theDSN memory 22 includes eight storage units 36, all eight storage unitsare located at the same site. As yet another example, if the DSN memory22 includes eight storage units 36, a first pair of storage units are ata first common site, a second pair of storage units are at a secondcommon site, a third pair of storage units are at a third common site,and a fourth pair of storage units are at a fourth common site. Notethat a DSN memory 22 may include more or less than eight storage units36. Further note that each storage unit 36 includes a computing core (asshown in FIG. 2, or components thereof) and a plurality of memorydevices for storing dispersed error encoded data.

Each of the computing devices 12-16, the managing unit 18, and theintegrity processing unit 20 include a computing core 26, which includesnetwork interfaces 30-33. Computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each of the managing unit 18 and the integrity processing unit20 may be separate computing devices, may be a common computing device,and/or may be integrated into one or more of the computing devices 12-16and/or into one or more of the storage units 36.

Each interface 30, 32, and 33 includes software and hardware to supportone or more communication links via the network 24 indirectly and/ordirectly. For example, interface 30 supports a communication link (e.g.,wired, wireless, direct, via a LAN, via the network 24, etc.) betweencomputing devices 14 and 16. As another example, interface 32 supportscommunication links (e.g., a wired connection, a wireless connection, aLAN connection, and/or any other type of connection to/from the network24) between computing devices 12 & 16 and the DSN memory 22. As yetanother example, interface 33 supports a communication link for each ofthe managing unit 18 and the integrity processing unit 20 to the network24.

Computing devices 12 and 16 include a dispersed storage (DS) clientmodule 34, which enables the computing device to dispersed storage errorencode and decode data as subsequently described with reference to oneor more of FIGS. 3-8. In this example embodiment, computing device 16functions as a dispersed storage processing agent for computing device14. In this role, computing device 16 dispersed storage error encodesand decodes data on behalf of computing device 14. With the use ofdispersed storage error encoding and decoding, the DSN 10 is tolerant ofa significant number of storage unit failures (the number of failures isbased on parameters of the dispersed storage error encoding function)without loss of data and without the need for a redundant or backupcopies of the data. Further, the DSN 10 stores data for an indefiniteperiod of time without data loss and in a secure manner (e.g., thesystem is very resistant to unauthorized attempts at accessing thedata).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-14 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSN memory 22 fora user device, a group of devices, or for public access and establishesper vault dispersed storage (DS) error encoding parameters for a vault.The managing unit 18 facilitates storage of DS error encoding parametersfor each vault by updating registry information of the DSN 10, where theregistry information may be stored in the DSN memory 22, a computingdevice 12-16, the managing unit 18, and/or the integrity processing unit20.

The DSN managing unit 18 creates and stores user profile information(e.g., an access control list (ACL)) in local memory and/or withinmemory of the DSN module 22. The user profile information includesauthentication information, permissions, and/or the security parameters.The security parameters may include encryption/decryption scheme, one ormore encryption keys, key generation scheme, and/or dataencoding/decoding scheme.

The DSN managing unit 18 creates billing information for a particularuser, a user group, a vault access, public vault access, etc. Forinstance, the DSN managing unit 18 tracks the number of times a useraccesses a non-public vault and/or public vaults, which can be used togenerate a per-access billing information. In another instance, the DSNmanaging unit 18 tracks the amount of data stored and/or retrieved by auser device and/or a user group, which can be used to generate aper-data-amount billing information.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network administration includesmonitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

The integrity processing unit 20 performs rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. For retrieved encoded slices, they are checked for errors dueto data corruption, outdated version, etc. If a slice includes an error,it is flagged as a ‘bad’ slice. For encoded data slices that were notreceived and/or not listed, they are flagged as missing slices. Badand/or missing slices are subsequently rebuilt using other retrievedencoded data slices that are deemed to be good slices to produce rebuiltslices. The rebuilt slices are stored in the DSN memory 22.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the IO deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. The dispersed storage error encodingparameters include an encoding function (e.g., information dispersalalgorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R) of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides the data(e.g., a file (e.g., text, video, audio, etc.), a data object, or otherdata arrangement) into a plurality of fixed sized data segments (e.g., 1through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more).The number of data segments created is dependent of the size of the dataand the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 60 is shown inFIG. 6. As shown, the slice name (SN) 60 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as, at least part of, a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

To recover a data segment from a decode threshold number of encoded dataslices, the computing device uses a decoding function as shown in FIG.8. As shown, the decoding function is essentially an inverse of theencoding function of FIG. 4. The coded matrix includes a decodethreshold number of rows (e.g., three in this example) and the decodingmatrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

FIG. 9 is a schematic block diagram 900 of an embodiment of adecentralized, or distributed, agreement protocol (DAP) 80 that may beimplemented by a computing device, a storage unit, and/or any otherdevice or unit of the DSN to determine where to store encoded dataslices or where to find stored encoded data slices. The DAP 80 includesa plurality of functional rating modules 81. Each of the functionalrating modules 81 includes a deterministic function 83, a normalizingfunction 85, and a scoring function 87.

Each functional rating module 81 receives, as inputs, a slice identifier82 and storage pool (SP) coefficients (e.g., a first functional ratingmodule 81-1 receives SP 1 coefficients “a” and b). Based on the inputs,where the SP coefficients are different for each functional ratingmodule 81, each functional rating module 81 generates a unique score 93(e.g., an alpha-numerical value, a numerical value, etc.). The rankingfunction 84 receives the unique scores 93 and orders them based on anordering function (e.g., highest to lowest, lowest to highest,alphabetical, etc.) and then selects one as a selected storage pool 86.Note that a storage pool includes one or more sets of storage units 86.Further note that the slice identifier 82 corresponds to a slice name orcommon attributes of set of slices names. For example, for a set ofencoded data slices, the slice identifier 120 specifies a data segmentnumber, a vault ID, and a data object ID, but leaves open ended, thepillar number. As another example, the slice identifier 82 specifies arange of slice names (e.g., 0000 0000 to FFFF FFFF).

As a specific example, the first functional module 81-1 receives theslice identifier 82 and SP coefficients for storage pool 1 of the DSN.The SP coefficients includes a first coefficient (e.g., “a”) and asecond coefficient (e.g., “b”). For example, the first coefficient is aunique identifier for the corresponding storage pool (e.g., SP #1's IDfor SP 1 coefficient “a”) and the second coefficient is a weightingfactor for the storage pool. The weighting factors are derived toensure, over time, data is stored in the storage pools in a fair anddistributed manner based on the capabilities of the storage units withinthe storage pools.

For example, the weighting factor includes an arbitrary bias whichadjusts a proportion of selections to an associated location such that aprobability that a source name will be mapped to that location is equalto the location weight divided by a sum of all location weights for alllocations of comparison (e.g., locations correspond to storage units).As a specific example, each storage pool is associated with a locationweight factor based on storage capacity such that, storage pools withmore storage capacity have a higher location weighting factor thanstorage pools with less storage capacity.

The deterministic function 83, which may be a hashing function, ahash-based message authentication code function, a mask generatingfunction, a cyclic redundancy code function, hashing module of a numberof locations, consistent hashing, rendezvous hashing, and/or a spongefunction, performs a deterministic function on a combination and/orconcatenation (e.g., add, append, interleave) of the slice identifier 82and the first SP coefficient (e.g., SU 1 coefficient “a”) to produce aninterim result 89.

The normalizing function 85 normalizes the interim result 89 to producea normalized interim result 91. For instance, the normalizing function85 divides the interim result 89 by a number of possible outputpermutations of the deterministic function 83 to produce the normalizedinterim result. For example, if the interim result is 4,325 (decimal)and the number of possible output permutations is 10,000, then thenormalized result is 0.4325.

The scoring function 87 performs a mathematical function on thenormalized result 91 to produce the score 93. The mathematical functionmay be division, multiplication, addition, subtraction, a combinationthereof, and/or any mathematical operation. For example, the scoringfunction divides the second SP coefficient (e.g., SP 1 coefficient “b”)by the negative log of the normalized result (e.g., e^(y)=x and/orln(x)=y). For example, if the second SP coefficient is 17.5 and thenegative log of the normalized result is 1.5411 (e.g., e^((0.4235))),the score is 11.3555.

The ranking function 84 receives the scores 93 from each of the functionrating modules 81 and orders them to produce a ranking of the storagepools. For example, if the ordering is highest to lowest and there arefive storage units in the DSN, the ranking function evaluates the scoresfor five storage units to place them in a ranked order. From theranking, the ranking module 84 selects one the storage pools 86, whichis the target for a set of encoded data slices.

The DAP 80 may further be used to identify a set of storage units, anindividual storage unit, and/or a memory device within the storage unit.To achieve different output results, the coefficients are changedaccording to the desired location information. The DAP 80 may alsooutput the ranked ordering of the scores.

FIG. 10 is a schematic block diagram 1000 of an example of creatingpluralities of sets of slices. Each plurality of sets of encoded dataslices (EDSs) corresponds to the encoding of a data object, a portion ofa data object, or multiple data object, where a data object is one ormore of a file, text, data, digital information, etc. For example, thehighlighted plurality of encoded data slices corresponds to a dataobject having a data identifier of “a2”.

Each encoded data slices of each set of encoded data slices is uniquelyidentified by its slice name, which is also used as at least part of theDSN address for storing the encoded data slice. As shown, a set of EDSsincludes EDS 1_1_1_a1 through EDS 5_1_1_a1. The EDS number includespillar number, data segment number, vault ID, and data object ID. Thus,for EDS 1_1_1_a1, it is the first EDS of a first data segment of dataobject “a1” and is to be stored, or is stored, in vault 1. Note thatvaults are a logical memory container supported by the storage units ofthe DSN. A vault may be allocated to one or more user computing devices.

As is further shown, another plurality of sets of encoded data slicesare stored in vault 2 for data object “b1”. There are Y sets of EDSs,where Y corresponds to the number of data segments created by segmentingthe data object. The last set of EDSs of data object “b1” includes EDS1_Y_2_b1 through EDS 5_Y_2_b1. Thus, for EDS 1_Y_2_b1, it is the firstEDS of the last data segment “Y” of data object “b1” and is to bestored, or is stored, in vault 2.

FIG. 11 is a schematic block diagram 1100 of an example of storagevaults spanning multiple storage pools. In this example, the DSN memory22 includes a plurality of storage units 36 arranged into a plurality ofstorage pools (e.g., 1-n). In this example, each storage pool includesseven storage units for ease of illustration. A storage pool, however,can have many more storage units than seven and, from storage pool tostorage pool, may have different numbers of storage units.

The storage pools 1-n support two vaults (vault 1 and vault 2) usingonly five of seven of the storage units. The number of storage unitswithin a vault correspond to the pillar width number, which is five inthis example. Note that a storage pool may have rows of storage units,where SU #1 represents a plurality of storage units, each correspondingto a first pillar number; SU #2 represents a second plurality of storageunits, each corresponding to a second pillar number; and so on. Notethat other vaults may use more or less than a width of five storageunits.

FIG. 12 is a schematic block diagram 1200 of an example of storingpluralities of sets of slices in accordance with the Decentralized, orDistributed, Agreement Protocol (DAP) 80 of FIG. 9. The DAP 80 usesslice identifiers (e.g., the slice name or common elements thereof(e.g., the pillar number, the data segment number, the vault ID, and/orthe data object ID)) to identify, for one or more sets of encoded dataslices, a set, or pool, of storage units. With respect to the threepluralities of sets of encoded data slices (EDSs) of FIG. 11, the DAP 80approximately equally distributes the sets of encoded data slicesthroughout the DSN memory (e.g., among the various storage units).

The first column corresponds to storage units having a designation of SU#1 in their respective storage pool or set of storage units and storesencoded data slices having a pillar number of 1. The second columncorresponds to storage units having a designation of SU #2 in theirrespective storage pool or set of storage units and stores encoded dataslices having a pillar number of 2, and so on. Each column of EDSs isdivided into one or more groups of EDSs. The delineation of a group ofEDSs may correspond to a storage unit, to one or more memory deviceswithin a storage unit, or multiple storage units. Note that the groupingof EDSs allows for bulk addressing, which reduces network traffic.

A range of encoded data slices (EDSs) spans a portion of a group, spansa group, or spans multiple groups. The range may be numerical range ofslice names regarding the EDSs, one or more source names (e.g., commonaspect shared by multiple slice names), a sequence of slice names, orother slice selection criteria.

FIG. 13 is a schematic block diagram 1300 of an example of adding astorage pool to the DSN. In this example storage pool n+1 is added andis supporting vaults 1 and 2. As result, the Decentralized, orDistributed, Agreement Protocol (DAP) 80 of FIG. 9 is changed to includeanother functional rating module 81 for the new storage pool and thesecond coefficients (e.g., “b”, which correspond to the weight factor)are adjusted for some, if not all, of the other functional ratingmodules 81. As a result of changing the DAP 80, storage responsibilityfor encoded data slices is going to change, causing them to betransferred between the storage units. When there are significantnumbers of encoded data slices to be transferred and there are hundredsto tens of thousands of resources in the DSN (e.g., computing devices,storage units, managing units, integrity units performing rebuilding,etc.), the updating of the DSN is complex and time consuming.

While the DSN is being updated based on the new DAP, data accessrequests, listing requests, and other types of requests regarding theencoded data slices are still going to be received and need to beprocessed in a timely manner. Such requests will be based on the oldDAP. As such, a request for an encoded data slice (EDS), or informationabout the EDS, will go to the storage unit identified using the DAP 80prior to updating it. If the storage unit has already transferred theEDS to the storage unit identified using the new DAP 80, then thestorage unit functions as proxy for the new storage unit and therequesting device.

FIG. 14 is a schematic block diagram of an embodiment 1400 of adecentralized, or distributed, agreement protocol (DAP) for generatingidentified set of storage units in accordance with the presentinvention. The DAP 80 is similar to the DAP of FIG. 9, but uses a sliceidentifier 120 instead of a source name 82, uses coefficients for a setof storage units instead of for individual storage units, and theranking function 84 outputs an identified set of storage units 122instead of a storage unit ranking 86. The slice identifier 120corresponds to a slice name or common attributes of set of slices names.For example, for a set of encoded data slices, the slice identifier 120specifies a data segment number, a vault ID, and a data object ID, butleaves open ended, the pillar number.

In an example of the operation, each of the functional rating modules 81generates a score 93 for each set of the storage units based on theslice identifier 120. The ranking function 84 orders the scores 93 toproduce a ranking. But, instead of outputting the ranking, the rankingfunction 84 outputs one of the scores, which corresponds to theidentified set of storage units.

As can be seen, such a DAP may be implemented and executed for manydifferent applications including for the determination of where to storeencoded data slices or where to find stored encoded data slices such aswith respect to FIG. 9 as well as the identification of a set of storageunits (SUs) such as with respect to FIG. 14. Based on differentlyprovided input to the DAP, differently provided information may beoutput. Generally speaking, the more detailed information is that isprovided to the DAP, then the more detailed information will be outputwhen from the DAP when executed.

FIG. 15 is a schematic block diagram of an example 1500 of a replacementof a storage unit (SU) within a storage pool in accordance with thepresent invention. A storage pol includes a plurality of storage units(SUs) (e.g., shown as SU #1 36 through SU #x 36 through SU #y 36 throughSU #z 36), each respectively storing information such as slice name (SN)and encoded data slice (EDS) for a plurality of slices of at least apillar width (e.g., the slices are shown as being stored respectivelyacross the SUs such that a respective SN and EDS is shown as beingstored within each respective SU).

From certain perspectives, EDS sets that correspond respectively to datasegments of a data object are distributedly stored across the pluralityof storage units SUs within the DSN (e.g., shown in this example 1500 asacross the plurality of SUs of a storage pool). The data object issegmented into the plurality of data segments, and a data segment of theplurality of data segments is dispersed error encoded in accordance withdispersed error encoding parameters to produce a set of EDSs of the EDSsets that is of pillar width having a plurality of EDS names. A readthreshold number of EDSs of the set of EDSs provides for reconstructionof the data segment, and a write threshold number of EDSs of the set ofEDSs provides for a successful transfer of the set of EDSs from a firstat least one location in the DSN to a second at least one location inthe DSN. The data object is associated with a unique source name, andeach EDS name of the plurality of EDS names includes a reference to theunique source name.

The SUs of the storage pool operate based on a DAP. For various reasons,the DAP may undergo a system configuration (e.g., expansion of thestorage pool by adding one or more SUs, removing one or more SUs fromthe storage pool, replacing one or more SUs within the storage pool,modification of one or more dispersed error encoding parameters, etc.).For example, in a DSN memory, storage capacity may be added to expandthe storage pool by adding one a SU (or SU set) to it.

In an example of operation and implementation, a computing device isconfigured to operate to monitor for a change of system configuration ofthe DAP (e.g., from a first to a second system configuration of theDAP). Alternatively, a computing device may be configured to receive anotification of a change of system configuration of the DAP. In anotherexample, a computing device is configured to poll another device forinformation regarding a change of system configuration of the DAP.Regardless of the manner by which the computing device may be informedof a change of system configuration of the DAP, the computing deviceoperates to detect a change from a first system configuration of aDecentralized, or Distributed, Agreement Protocol (DAP) to a secondsystem configuration of the DAP to a second system configuration of theDAP. Such a change may be precipitated based on addition or removal ofat least one SU within a plurality of SUs within the DSN (e.g., within astorage pool of the DSN).

As described herein, the first system configuration of the DAP and thesecond system configuration of the DAP respectively provide fordeterministic calculation of locations of encoded data slice (EDS) setsthat correspond respectively to a plurality of data segments of a dataobject that are distributedly stored across the plurality of storageunits SUs within the DSN (e.g., within the storage pool of the DSN).

The computing device detects a change from a first system configurationof the DAP to a second system configuration of the DAP based on astorage unit to be replaced (SUTBR) (e.g., shown as SU# x 36) within SUswithin the DSN (e.g., within the storage pool of the DSN). Again, thefirst system configuration of the DAP and the second systemconfiguration of the DAP respectively provide for deterministiccalculation of locations of EDS sets that correspond respectively to aplurality of data segments of a data object that are distributedlystored SUs within the DSN (e.g., within the storage pool of the DSN).The computing device then directs the SUTBR to transfer a plurality ofEDSs stored within the SUTBR to a replacement storage unit (RSU) (e.g.,shown as SU# x′ 36) for storage within the RSU.

During transfer of the plurality of EDSs from the SUTBR to the RSU, thecomputing device directs the plurality of SUs to operate based on thefirst system configuration of the DAP. Also, in some examples, thecomputing device directs the SUTBR to service read requests and writerequests from one or more other computing devices for at least one EDSof the plurality of EDSs based on the first system configuration of theDAP during transfer of the plurality of EDSs from the SUTBR to the RSU.

Then, when the plurality of EDSs have been successfully transferred fromthe SUTBR to the RSU, the computing device directs the plurality of SUsto operate based on the second system configuration of the DAP. Also, insome examples, the computing device directs the direct the RSU toservice read and write requests from the one or more other computingdevices for the at least one EDS of the plurality of EDSs based on thesecond system configuration of the DAP when the plurality of EDSs havebeen successfully transferred from the SUTBR to the RSU.

FIG. 16A, FIG. 16B, and FIG. 16C are schematic block diagrams 1601,2602, and 1603 of examples of replacement of a SU within a storage poolin accordance with the present invention.

In some examples and from some perspectives, the update of the systemconfiguration of the DAP from the first system configuration to thesecond system configuration, reallocation of EDSs may be viewed as aprocess by which a DAP is used to reallocate (e.g., migrate in someinstances) EDSs from one location to another (e.g., from one SU toanother, such as from the SUTBR to the RSU). In some embodiments, thiscan be used to reallocate EDS between SU sets (storage pool(s)) within agiven storage pool. For example, such a reallocation process may be usedbased on the addition, removal, and/or replacement of SU resources fromstorage pools in the increment of adding, removing, and/or replacing SUsets (storage pool(s)).

Note that when a SU is to be replaced (e.g., SUTBR to be replaced by theRSU), the reallocation process can require rebuilding of EDSs. Also,this may involve an off-line physical transfer of EDSs or memory devices(e.g., SUs) from the old SU to the new SU (from the SUTBR to the RSU).However, the reallocation process can also be used to handle SUreplacement in a more effective manner as described herein.

Referring to example 1601 of FIG. 16A, the SU set (storage pool) andstorage pool that contain the SUTBR are identified (e.g., the storagepool (plurality of SUs) that include the SU #x 36, which is the SUTBR).Then, a modified version of the storage resource map (SRM) for thestorage pool is created. Based on this, the SU set (storage pool)containing the SUTBR will have its respective weight set to “0” therein,and a new SU set (e.g., that includes the RSU) is created, having aweight set to “X” therein equal to the previous weight of the SU set(storage pool) containing the SUTBR (e.g., set to “X” therein). Then,the new SU set (storage pool) contains all the same devices as the priorSU set (storage pool) containing the SUTBR, except the entry for theSUTBR is replaced with the entry for the RSU. Also, the RSU will havethe same “hash seed” as the SUTBR that now will now have its respectiveweight set to “0” therein. A reallocation process is triggered from theold SRM to the newly modified SRM that contains the RSU, the modifiedweights, and the SU set (storage pool) having the RSU replaced with theSUTBR.

As the reallocation proceeds, all other SUs, aside from the SUTBR,discover that they do not have any anything (e.g., any EDSs) to transferas they are not in the changed SU set (storage pool) and because therewere no weight changes for the total of all SU sets with the same hashseed. Alternatively, all other SUs, aside from the SUTBR, discover thatthey do not have any anything (e.g., any EDSs) to transfer because theSU without which they would be reallocating EDSs in the new SU set(storage pool) is itself (e.g., the same SU set (storage pool)). Basedon this, each SU in the modified, new SU set (storage pool) discoversthis fact, except for the replaced device).

The SUTBR, however, finds that it is in a SU set (storage pool) with azero weight, and that the destination it should move its EDSs to is a SUdifferent from itself. It therefore ends up transferring all of its EDSsto the RSU in the new SU set (storage pool). Also, in some examples,note that the SUTBR remains fully online throughout, responds to readrequests, and stores write requests, and the entire process of updatecompletes without any rebuilding.

In some examples, note that the DAP, when executed using the uniquesource name and coefficients regarding the plurality of SUs of the DSN,produces a ranking of the plurality of SUs that deterministicallyidentifies those SUs of the plurality of SUs that store the EDS setsincluding the set of EDSs of the EDS sets. In an example of operationand implementation, computing device updates the coefficients regardingthe plurality of SUs based on the change from the first systemconfiguration of the DAP to the second system configuration of the DAP.

In another example of operation and implementation, the computing deviceidentifies a storage resource map (SRM) for the plurality of SUsincluding the SUTBR. Then, when the plurality of EDSs have beensuccessfully transferred from the SUTBR to the RSU, the computing deviceupdates the SRM by replacing a first entry associated with the SUTBRwith a second entry associated with the RSU.

Referring to example 1602 of FIG. 16B, in this example of operation andimplementation, the computing device directs the SUTBR (e.g., SU #x 36)to respond to a read request from another computing device for the atleast one EDS of the plurality of EDSs by providing the at least one EDSof the plurality of EDSs stored within the SUTBR (e.g., SU #x 36) to theanother computing device during transfer of the plurality of EDSs fromthe SUTBR to the RSU based on the first system configuration of the DAP.Then, after the plurality of EDSs have been successfully transferredfrom the SUTBR to the RSU based on the update of the DAP from the firstsystem configuration of the DAP to the second system configuration ofthe DAP, the computing device directs the RSU (e.g., SU #x′ 36) torespond to a read request from another computing device for the at leastone EDS of the plurality of EDSs by providing the at least one EDS ofthe plurality of EDSs stored within the RSU (e.g., SU #x′ 36) to theanother computing device during transfer of the plurality of EDSs fromthe SUTBR to the RSU based on the second system configuration of theDAP.

Referring to example 1603 of FIG. 16C, in this example of operation andimplementation, the computing device directs the SUTBR (e.g., SU #x 36)to respond to a write request from another computing device to write theat least one EDS of the plurality of EDSs by storing the write requestfrom the another computing device during transfer of the plurality ofEDSs from the SUTBR to the RSU (e.g., SU #x′ 36). Then, the computingdevice directs the SUTBR (e.g., SU #x 36) to provide the write requestthat has been stored in the SUTBR (e.g., SU #x 36) from the SUTBR (e.g.,SU #x 36) to the RSU when the plurality of EDSs have been successfullytransferred from the SUTBR to the RSU for storage of the at least oneEDS of the plurality of EDSs within the RSU based on the second systemconfiguration of the DAP.

In some examples, the computing device is located at a first premisesthat is remotely located from at least one SU of the plurality of SUswithin the DSN. In other examples, the computing device may itself be aSU of the plurality of SUs within the DSN. Alternatively, the computingdevice is a wireless smart phone, a laptop, a tablet, a personalcomputers (PC), a work station, and/or a video game device. Note alsothat the DSN may be implemented to include a wireless communicationsystem, a wire lined communication systems, a non-public intranetsystem, a public internet system, a local area network (LAN), and/or awide area network (WAN).

FIG. 17 is a diagram illustrating an embodiment of a method 1700 forexecution by one or more computing devices. In some optional examples,the method 1700 operates by monitoring for a change of systemconfiguration of the DAP (e.g., from a first to a second systemconfiguration of the DAP) (block 1710). Alternatively, the method 1700may operate by receiving a notification of a change of systemconfiguration of the DAP. In another example, the method 1700 mayoperate by polling another device for information regarding a change ofsystem configuration of the DAP. Regardless of the manner by which themethod 1700 is informed of a change of system configuration of the DAP,the method 1700 operates by detecting a change from a first systemconfiguration of a Decentralized, or Distributed, Agreement Protocol(DAP) to a second system configuration of the DAP to a second systemconfiguration of the DAP. Such a change may be precipitated based onaddition or removal of at least one SU within a plurality of SUs withinthe DSN (e.g., within a storage pool of the DSN).

When the method 1700 operates by detecting no change of from a firstsystem configuration of the DAP to a second system configuration of theDAP to a second system configuration of the DAP (block 1720), the method1700 ends or continues monitoring for a change, update, etc. (e.g.,loops back to block 1710). Alternatively, when the method 1700 operatesby detecting a change of from the first system configuration of the DAPto the second system configuration of the DAP to a second systemconfiguration of the DAP (block 1720), the method 1700 operates bydirecting a storage unit to be replaced (SUTBR) to transfer a pluralityof EDSs stored within the SUTBR to a replacement storage unit (RSU) forstorage within the RSU (block 1730). Note that this detection of achange of from the first system configuration of the DAP to the secondsystem configuration of the DAP to a second system configuration of theDAP may be based on a SUTBR within a plurality of storage units (SUs)within a dispersed storage network (DSN) to be replaced by a replacementstorage unit (RSU).

The, during transfer of the plurality of EDSs from the SUTBR to the RSU(e.g., during update from the first system configuration of the DAP tothe second system configuration of the DAP), the method 1700 operates bydirecting the plurality of SUs to operate based on the first systemconfiguration of the DAP (block 1740). Also, in some examples, themethod 1700 operates by directing the SUTBR to service read requests andwrite requests from one or more other computing devices for at least oneEDS of the plurality of EDSs based on the first system configuration ofthe DAP (block 1742).

The method 1700 then operates by monitoring for whether the plurality ofEDSs having been successfully transferred from the SUTBR to the RSU(e.g., monitor for successful update from the first system configurationof the DAP to the second system configuration of the DAP) (block 1750).During the transfer of the plurality of EDSs from the SUTBR to the RSU(e.g., during update from the first system configuration of the DAP tothe second system configuration of the DAP), the method 1700 will loopback to the monitoring of block 1750.

However, when the method 1700 operates by detecting that the pluralityof EDSs have been successfully transferred from the SUTBR to the RSU(e.g., a successful update from the first system configuration of theDAP to the second system configuration of the DAP has been detected)(block 1760), then the method 1700 operates by directing the pluralityof SUs to operate based on the second system configuration of the DAP(block 1770). Also, in some examples, the method 1700 operates bydirecting the RSU to service read and write requests from the one ormore other computing devices for the at least one EDS of the pluralityof EDSs based on the second system configuration of the DAP (block1772).

In some examples, the basis for determining the plurality of EDSs havebeen successfully transferred from the SUTBR to the RSU (e.g., asuccessful update from the first system configuration of the DAP to thesecond system configuration of the DAP has been detected) may be a writethreshold number of EDSs of the set of EDSs such that the writethreshold number of EDSs provides for a successful transfer of the setof EDSs from a first at least one location in the DSN to a second atleast one location in the DSN.

It is noted that terminologies as may be used herein such as bit stream,stream, signal sequence, etc. (or their equivalents) have been usedinterchangeably to describe digital information whose contentcorresponds to any of a number of desired types (e.g., data, video,speech, audio, etc. any of which may generally be referred to as‘data’).

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from figureto figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A computing device comprising: an interfaceconfigured to interface and communicate with a dispersed storage network(DSN); memory that stores operational instructions; and a processingmodule operably coupled to the interface and to the memory, wherein theprocessing module, when operable within the computing device based onthe operational instructions, is configured to: detect a change from afirst system configuration of a Decentralized, or Distributed, AgreementProtocol (DAP) to a second system configuration of the DAP based on astorage unit to be replaced (SUTBR) within a plurality of storage units(SUs) within the DSN, wherein the first system configuration of the DAPand the second system configuration of the DAP respectively provide fordeterministic calculation of locations of encoded data slice (EDS) setsthat correspond respectively to a plurality of data segments of a dataobject that are distributedly stored across the plurality of storageunits (SUs) within the DSN, wherein the data object is segmented intothe plurality of data segments, wherein a data segment of the pluralityof data segments is dispersed error encoded in accordance with dispersederror encoding parameters to produce a set of EDSs of the EDS sets thatis of pillar width having a plurality of EDS names, wherein a readthreshold number of EDSs of the set of EDSs provides for reconstructionof the data segment, wherein a write threshold number of EDSs of the setof EDSs provides for a successful transfer of the set of EDSs from afirst at least one location in the DSN to a second at least one locationin the DSN, wherein the data object is associated with a unique sourcename, and wherein each EDS name of the plurality of EDS names includes areference to the unique source name; direct the SUTBR to transfer aplurality of EDSs stored within the SUTBR to a replacement storage unit(RSU) for storage within the RSU; during transfer of the plurality ofEDSs from the SUTBR to the RSU: direct the plurality of SUs to operatebased on the first system configuration of the DAP; and direct the SUTBRto service read requests and write requests from one or more othercomputing devices for at least one EDS of the plurality of EDSs based onthe first system configuration of the DAP; and when the plurality ofEDSs have been successfully transferred from the SUTBR to the RSU:direct the plurality of SUs to operate based on the second systemconfiguration of the DAP; and direct the RSU to service read and writerequests from the one or more other computing devices for the at leastone EDS of the plurality of EDSs based on the second systemconfiguration of the DAP.
 2. The computing device of claim 1, wherein:the DAP, when executed using the unique source name and coefficientsregarding the plurality of SUs of the DSN, produces a ranking of theplurality of SUs that deterministically identifies those SUs of theplurality of SUs that store the EDS sets including the set of EDSs ofthe EDS sets; and the processing module, when operable within thecomputing device based on the operational instructions, is furtherconfigured to update the coefficients regarding the plurality of SUsbased on the change from the first system configuration of the DAP tothe second system configuration of the DAP.
 3. The computing device ofclaim 1, wherein the processing module, when operable within thecomputing device based on the operational instructions, is furtherconfigured to: identify a storage resource map (SRM) for the pluralityof SUs including the SUTBR; and when the plurality of EDSs have beensuccessfully transferred from the SUTBR to the RSU, update the SRM byreplacing a first entry associated with the SUTBR with a second entryassociated with the RSU.
 4. The computing device of claim 1, wherein theprocessing module, when operable within the computing device based onthe operational instructions, is further configured to: direct the SUTBRto respond to a read request from another computing device for the atleast one EDS of the plurality of EDSs by providing the at least one EDSof the plurality of EDSs stored within the SUTBR to the anothercomputing device during transfer of the plurality of EDSs from the SUTBRto the RSU based on the first system configuration of the DAP.
 5. Thecomputing device of claim 1, wherein the processing module, whenoperable within the computing device based on the operationalinstructions, is further configured to: direct the SUTBR to respond to awrite request from another computing device to write the at least oneEDS of the plurality of EDSs by storing the write request from theanother computing device during transfer of the plurality of EDSs fromthe SUTBR to the RSU; and direct the SUTBR to provide the write requestthat has been stored in the SUTBR from the SUTBR to the RSU when theplurality of EDSs have been successfully transferred from the SUTBR tothe RSU for storage of the at least one EDS of the plurality of EDSswithin the RSU based on the second system configuration of the DAP. 6.The computing device of claim 1, wherein the computing device is locatedat a first premises that is remotely located from at least one SU of theplurality of SUs within the DSN.
 7. The computing device of claim 1further comprising: a SU of the plurality of SUs within the DSN.
 8. Thecomputing device of claim 1 further comprising: a wireless smart phone,a laptop, a tablet, a personal computers (PC), a work station, or avideo game device.
 9. The computing device of claim 1, wherein the DSNincludes at least one of a wireless communication system, a wire linedcommunication system, a non-public intranet system, a public internetsystem, a local area network (LAN), or a wide area network (WAN).
 10. Amethod for execution by a computing device, the method comprising:detecting a change from a first system configuration of a Decentralized,or Distributed, Agreement Protocol (DAP) to a second systemconfiguration of the DAP based on a storage unit to be replaced (SUTBR)within a plurality of storage units (SUs) within a dispersed storagenetwork (DSN), wherein the first system configuration of the DAP and thesecond system configuration of the DAP respectively provide fordeterministic calculation of locations of encoded data slice (EDS) setsthat correspond respectively to a plurality of data segments of a dataobject that are distributedly stored across the plurality of storageunits (SUs) within the DSN, wherein the data object is segmented intothe plurality of data segments, wherein a data segment of the pluralityof data segments is dispersed error encoded in accordance with dispersederror encoding parameters to produce a set of EDSs of the EDS sets thatis of pillar width having a plurality of EDS names, wherein a readthreshold number of EDSs of the set of EDSs provides for reconstructionof the data segment, wherein a write threshold number of EDSs of the setof EDSs provides for a successful transfer of the set of EDSs from afirst at least one location in the DSN to a second at least one locationin the DSN, wherein the data object is associated with a unique sourcename, and wherein each EDS name of the plurality of EDS names includes areference to the unique source name; directing the SUTBR to transfer aplurality of EDSs stored within the SUTBR to a replacement storage unit(RSU) for storage within the RSU; during transfer of the plurality ofEDSs from the SUTBR to the RSU: directing the plurality of SUs tooperate based on the first system configuration of the DAP; anddirecting the SUTBR to service read requests and write requests from oneor more other computing devices for at least one EDS of the plurality ofEDSs based on the first system configuration of the DAP; and when theplurality of EDSs have been successfully transferred from the SUTBR tothe RSU: directing the plurality of SUs to operate based on the secondsystem configuration of the DAP; and directing the RSU to service readand write requests from the one or more other computing devices for theat least one EDS of the plurality of EDSs based on the second systemconfiguration of the DAP.
 11. The method of claim 10, wherein: the DAP,when executed using the unique source name and coefficients regardingthe plurality of SUs of the DSN, produces a ranking of the plurality ofSUs that deterministically identifies those SUs of the plurality of SUsthat store the EDS sets including the set of EDSs of the EDS sets; andfurther comprising: updating the coefficients regarding the plurality ofSUs based on the change from the first system configuration of the DAPto the second system configuration of the DAP.
 12. The method of claim10 further comprising: identifying a storage resource map (SRM) for theplurality of SUs including the SUTBR; and when the plurality of EDSshave been successfully transferred from the SUTBR to the RSU, updatingthe SRM by replacing a first entry associated with the SUTBR with asecond entry associated with the RSU.
 13. The method of claim 10 furthercomprising: directing the SUTBR to respond to a read request fromanother computing device for the at least one EDS of the plurality ofEDSs by providing the at least one EDS of the plurality of EDSs storedwithin the SUTBR to the another computing device during transfer of theplurality of EDSs from the SUTBR to the RSU based on the first systemconfiguration of the DAP.
 14. The method of claim 10 further comprising:directing the SUTBR to respond to a write request from another computingdevice to write the at least one EDS of the plurality of EDSs by storingthe write request from the another computing device during transfer ofthe plurality of EDSs from the SUTBR to the RSU; and directing the SUTBRto provide the write request that has been stored in the SUTBR from theSUTBR to the RSU when the plurality of EDSs have been successfullytransferred from the SUTBR to the RSU for storage of the at least oneEDS of the plurality of EDSs within the RSU based on the second systemconfiguration of the DAP.
 15. The method of claim 10, wherein thecomputing device is located at a first premises that is remotely locatedfrom at least one SU of the plurality of SUs within the DSN.
 16. Themethod of claim 10, wherein the computing device includes a SU of theplurality of SUs within the DSN.
 17. The method of claim 10, wherein thecomputing device includes a wireless smart phone, a laptop, a tablet, apersonal computers (PC), a work station, or a video game device.
 18. Themethod of claim 10, wherein the DSN includes at least one of a wirelesscommunication system, a wire lined communication system, a non-publicintranet system, a public internet system, a local area network (LAN),or a wide area network (WAN).